Subj : Re: win32 - High speed serial streaming code???
To   : comp.programming
From : DarkD
Date : Thu Sep 01 2005 05:54 pm


<robertwessel2@yahoo.com> wrote in message
news:1125554723.399493.269650@g14g2000cwa.googlegroups.com...
>
> DarkD wrote:
> > I need to capture data from a serial device that has 115200bps output.
Its
> > continously outputs 3byte packets 1250 times per second.
> >
> > I have tried using the win standard way to do serial port access
(CreateFile
> > ReadFile etc.) and cannot obtain anywhere near 3750 bytes per second.
The
> > system is completely dropping some data.
> >
> > The 3rd byte in every packet is 0xFF and the packets can have no break
in
> > time between the 3rd byte of one and the first of the next. I am not
sure if
> > 0xFF is affecting anything. Alot of the packets are: 0x00 0x00 0xFF, so
im
> > not sure if this is cuasing the problem either.
> >
> > I have tried use setupcomm to give massive buffers (30KB etc.) and can't
get
> > close to 3750 bytes per second
> > .
> > With ReadFile how many bytes should I be reading? If I put 3 I can get
about
> > 100 packets per second. If I put 1000bytes I get about 200 packets per
> > second...
> >
> > I am using visual c++
> >
> > I know it is not a CPU performance thing because this is a 3GHz P4 and
the
> > CPU usuage is zero all the time.
> >
> > Is there some other way to low level access the uart chip so I can
stream in
> > this data fully? I cannot understand why modern computer cannot
continously
> > stream and save data at 115200bps.
> >
> > I have also tried event based triggering and the performance is just as
bad.
>
>
> Something else is wrong.  On that fast a machine doing even one byte
> reads should be able to keep up with that with no problem whatsoever.

Thanks for your help. I found the problem to a bad cable that was stuffing
up most bits including the start/stop bits etc.

Now its working flawlessly. I have about 4 threads running, one just buffers
as fast as it can and one works off the buffer to convert data as it comes
and other grabs converted data for displaying etc.

.